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Abstract:

The present invention provides plain printing paper comprising a paper
substrate containing, as main components, cellulose pulp and calcium
carbonate as a filler, and an optional cationic resin and a multivalent
cation salt attached onto the paper substrate, wherein the total amount
of the cationic resin and the multivalent cation salt attached on both
surfaces of the paper substrate is 1.0 g/m2 to 5.0 g/m2, both
inclusive, and the mass ratio of the cationic resin to the multivalent
cation salt is 0:100 to 90:10, both inclusive.

Claims:

1. Plain printing paper comprising a paper substrate containing, as main
components, cellulose pulp and calcium carbonate as a filler, and an
optional cationic resin, and a multivalent cation salt attached onto the
paper substrate, wherein the total amount of the cationic resin and the
multivalent cation salt attached on both surfaces of the paper substrate
is 1.0 g/m2 to 5.0 g/m2, both inclusive, and the mass ratio of
the cationic resin to the multivalent cation salt is 0:100 to 90:10, both
inclusive.

2. The plain printing paper according to claim 1, wherein the mass ratio
of the cationic resin to the multivalent cation salt is 10:90 to 80:20,
both inclusive.

3. The plain printing paper according to claim 1, wherein the cationic
resin is dimethylamine-epichlorohydrin polycondensate.

4. The plain printing paper according to claim 1, wherein the multivalent
cation salt is a calcium salt.

5. The plain printing paper according to claim 4, wherein the calcium
salt is calcium chloride.

6. A method for forming printed images, comprising ink jet printing using
a pigment ink and the plain printing paper as set forth in claim 1 at a
printing speed of 60 m/min or more.

7. The plain printing paper according to claim 2, wherein the cationic
resin is dimethylamine-epichlorohydrin polycondensate.

8. The plain printing paper according to claim 2, wherein the multivalent
cation salt is a calcium salt.

9. The plain printing paper according to claim 3, wherein the multivalent
cation salt is a calcium salt.

10. A method for forming printed images, comprising ink jet printing
using a pigment ink and the plain printing paper as set forth in claim 2
at a printing speed of 60 m/min or more.

11. A method for forming printed images, comprising ink jet printing
using a pigment ink and the plain printing paper as set forth in claim 3
at a printing speed of 60 m/min or more.

12. A method for forming printed images, comprising ink jet printing
using a pigment ink and the plain printing paper as set forth in claim 4
at a printing speed of 60 m/min or more.

13. A method for forming printed images, comprising ink jet printing
using a pigment ink and the plain printing paper as set forth in claim 5
at a printing speed of 60 m/min or more.

Description:

TECHNICAL FIELD

[0001] The present invention relates to printing paper and a method for
forming printed images. In more detail, the invention relates to plain
printing paper and a method for forming printed images.

BACKGROUND ART

[0002] Ink jet recording which creates images using water-soluble inks has
made marked strides recently. Ink jet recording is a type of printing
that creates images and characters by ejecting small droplets of ink
based on various principles to allow them to land on recording sheets
such as paper. Ink jet recording is fast and quiet, facilitates
multicolor printing, is versatile in terms of recordable patterns, and is
free from the need of development or fixation. Thus, its use has become
rapidly widespread in various applications to enable printing machines to
print various figures including Chinese characters as well as color
images. Further, ink jet recording can produce images which stand
comparison with prints made by offset printing according to a printing
plate technique or by a color photographic technique. Furthermore, ink
jet recording has been widely used in the full color field because a
small number of copies can be printed more inexpensively than by offset
printing or a photographic technique.

[0003] As a result of further progress in the technology, ink jet
recording has recently become used in industrial printing (hereinafter,
referred to as "ink jet printing"). Because large numbers of copies are
printed in the industrial printing field, printing speed is important due
to the tradeoff between productivity and printing costs. A printing speed
suitable for ink jet printing is achieved with a printing machine that is
equipped with a line head in which ink-ejecting heads are fixed in the
entirety of the width direction perpendicular to the paper transport
direction (hereinafter, such a printing machine will be referred to as
"ink jet printing machine") (see, for example, Patent Literature 1). More
recently, rotary ink jet printing machines having a printing speed of 15
m/min or more, a higher speed of 60 m/min or more, and a still higher
speed in excess of 120 m/min have been developed. Rotary ink jet printing
machines are also utilized in on-demand printing applications such as
printing of addresses, printing of customer information, printing of
numbers, and printing of bar codes. Because ink jet printing machines
allow for handling of variable information, their use is particularly
found in on-demand printing. In such applications, a preferred manner of
industrial printing is to preliminarily print fixed information by offset
printing and to print variable information by ink jet printing.

[0004] The types of printing paper used for ink jet printing machines are
broadly categorized into so-called plain printing paper such as
high-quality paper and PPC paper, and coated printing paper having a
distinct ink receiving layer on a paper substrate.

[0005] Low-cost plain printing paper represents the overwhelming majority
of paper used for industrial ink jet printing machines. Frequent
applications of plain printing paper include invoices and account
statements, and ad-papers and direct mails, as well as a combination
thereof, namely, so-called transaction mail promotion. Because of the
absence of an ink-receiving layer, however, such plain printing paper is
poor in ink absorption properties compared to coated printing paper,
resulting in the occurrence of uneven printing.

[0006] Inks used in ink jet printing machines are more frequently aqueous
pigment inks replacing aqueous dye inks. The use of aqueous pigment inks
encounters different problems from those in the case of aqueous dye inks.

[0007] The water resistance of images has been an important quality
requirement in the use of aqueous dye inks. That is, the dye inks are
required not to spread under highly humid conditions or in the event
where the image is brought into contact with water for any reason.

[0008] On the other hand, the abrasion resistance of images is one of the
quality requirements in the use of aqueous pigment inks. If the abrasion
resistance of images is low, any friction on images after printing and
drying causes the pigment inks to become detached and smear the printed
images.

[0009] Uneven printing in printed sections is a problem encountered with
pigment inks. Uneven printing is a phenomenon in which printing paper
exhibits a nonuniform density of an ink fixed in the final printed image
after the ink is dried to cause uneven ink absorption properties during
high speed printing. Because inks used in ink jet printing have a low
concentration of color material, uneven printing tends to be more marked
than in offset printing. The presence of uneven printing deteriorates the
commercial value of prints.

[0010] Some types of plain-like ink jet recording paper are coated
slightly with silica to achieve a higher printing density (see, for
example, Patent Literatures 2 and 3). However, such recording paper is
poor in offset printability and does not reflect any consideration of
abrasion resistance. An improvement in printing density can be expected
with plain ink jet recording paper that is coated with PVA to control the
Stockigt sizing degree (see, for example, Patent Literature 4). However,
such recording paper is poor in abrasion resistance. Further, plain ink
jet recording paper coated with colloidal silica and PVA achieves
improved abrasion resistance (see, for example, Patent Literature 5), but
is unsatisfactory in terms of offset printability.

[0017] As mentioned above, existing plain printing paper does not satisfy
both of the suitability for offset printing and the suitability for ink
jet printing with aqueous dye inks and aqueous pigment inks.

[0018] A first object of the invention is that plain printing paper
satisfies the following requirements.

[0019] 1. To have good offset printability.

[0020] 2. To exhibit good ink absorption properties in ink jet printing
with respect to both of aqueous dye inks and aqueous pigment inks.

[0021] 3. To allow for high water resistance of images formed by ink jet
printing with aqueous dye inks.

[0022] 4. To allow for high abrasion resistance of images formed by ink
jet printing with aqueous pigment inks, and to sufficiently suppress the
occurrence of uneven printing during such printing.

[0023] A second object of the invention is to provide a method which can
form printed images without the occurrence of uneven printing even when
pigment inks are used for ink jet printing at a printing speed of 60
m/min or more.

[0024] A third object of the invention is to provide a method for forming
excellent printed images using an offset printing machine and/or an ink
jet printing machine.

Solution to Problem

[0025] That is, the invention provides printing paper comprising

[0026] a paper substrate containing, as main components, cellulose pulp
and calcium carbonate as a filler, and

[0029] the total amount of the cationic resin and the multivalent cation
salt attached on both surfaces of the paper substrate is 1.0 g/m2 to
5.0 g/m2, both inclusive, and the mass ratio of the cationic resin
to the multivalent cation salt is 0:100 to 90:10, both inclusive. Such
printing paper satisfies the first object, namely, has good offset
printability, exhibits good ink absorption properties in ink jet printing
with respect to both of aqueous dye inks and aqueous pigment inks, allows
for high water resistance of images formed by ink jet printing with
aqueous dye inks, and allows for high abrasion resistance of images
formed by ink jet printing with aqueous pigment inks and sufficiently
suppresses the occurrence of uneven printing during such printing. Thus,
the printing paper of the present invention may be suitably used in
industrial printing where fixed information is printed with an offset
printing machine and variable information is printed with an ink jet
printing machine.

[0030] Further, the invention provides a printing method using an ink jet
printing machine which comprises ink jet printing using a pigment ink on
the above printing paper at a printing speed of 60 m/min or more to form
a printed image. According to this method, printed images can be formed
without the occurrence of uneven printing even when ink jet printing is
performed at a printing speed of 60 m/min or more.

[0031] Furthermore, the invention provides a method which comprises
forming a printed image on the above printing paper using an offset
printing machine and/or an ink jet printing machine. According to this
method, excellent printed images can be formed using an offset printing
machine and/or an ink jet printing machine.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

[0032] As used herein, the term "ink jet printing machine" refers to an
industrial printing machine that is used in industrial printing utilizing
the ink jet recording technique. For example, such a printing machine is
an ink jet printing machine having a printing speed of 15 m/min or more,
a higher speed of 60 m/min or more, and a still higher speed in excess of
120 m/min, or a rotary ink jet printing machine using pigment inks. As
used herein, the term "ink jet printing machine' is distinguished from
ink jet recording printers having a printing speed of several meters per
minute such as small home printers and large format printers
(hereinafter, such printers will be referred to as "ink jet printers").
As used herein, the term "ink jet printing" refers to industrial printing
based on the ink jet recording technique using an ink jet printing
machine.

[0033] Offset printing is an indirect printing technique in which an ink
is transferred first to a blanket and then to a workpiece. To have good
offset printability means that no problems such as blanket piling are
found after offset printing.

[0034] Uneven printing is a phenomenon in which printing paper exhibits a
nonuniform density of an ink fixed in the final printed image after the
ink is dried to cause uneven ink absorption properties during high speed
printing.

[0035] Hereinbelow, the printing paper of the invention will be described
in detail.

[0036] The printing paper of the invention includes, as main components, a
paper substrate containing cellulose pulp and calcium carbonate as a
filler. The paper substrate used in the printing paper of the present
invention is a sheet containing cellulose pulp and a filler as main
components. Examples of the cellulose pulp include chemical pulps such as
LBKP (Leaf Bleached Kraft Pulp) and NBKP (Needle Bleached Kraft Pulp),
mechanical pulps such as GP (Groundwood Pulp), PGW (Pressure GroundWood
pulp), RMP (Refiner Mechanical Pulp), TMP (ThermoMechanical Pulp), CTMP
(ChemiThermoMechanical Pulp), CMP (ChemiMechanical Pulp) and CGP
(ChemiGroundwood Pulp), and waste paper pulps such as DIP (DeInked Pulp).
These pulps may be used singly or in any combination.

[0037] The calcium carbonate used as the filler in the present invention
may be precipitated calcium carbonate, ground calcium carbonate or both
in combination. Other fillers such as talc and kaolin may be additionally
used while still achieving the desired effects of the invention. In the
present invention, the paper substrate may contain the calcium carbonate
in an amount of 50 parts by mass or more relative to the total of
filler(s) in the substrate.

[0038] In addition to the cellulose pulp and the filler, the paper
substrate of the present invention may contain various additives such as
sizing agents, fixing agents, retention aids, cationizing agents and
paper strengthening additives. The paper substrate of the present
invention may be produced by mixing the cellulose pulp and the filler as
well as various additives such as sizing agents, fixing agents, retention
aids, cationizing agents and paper strengthening additives, and making
the resultant paper stock into paper with any of various papermaking
machines such as Fourdrinier machines, cylinder paper machines and twin
wire machines.

[0040] In the present invention, the sizing degree of the paper substrate
may be any sizing degree as long as the desired effects of the invention
are achieved. The sizing degree may be controlled by controlling the
amount of an internal sizing agent or the amount of a surface sizing
agent applied onto the paper substrate. Examples of the internal sizing
agents include rosin sizing agents for acid paper, and alkenyl succinic
acid anhydrides, alkyl ketene dimers, neutral rosin sizing agents and
cationic styrene-acrylic sizing agents for alkaline paper. Examples of
the surface sizing agents include styrene-acrylic sizing agents, olefin
sizing agents and styrene-maleic sizing agents. In particular, a cationic
or nonionic surface sizing agent is preferable when the sizing agent is
applied together with a cationic resin and a multivalent cation salt
described later.

[0041] From the viewpoints of absorptivity of ink jet inks and the
prevention of uneven printing, the ash content in the paper substrate is
preferably 8 mass % to 25 mass %, both inclusive. When the ash content is
8 mass % or more, the occurrence of uneven printing can be suppressed. An
ash content of 25 mass % or less ensures that the occurrence of troubles
such as picking and paper break during offset printing ascribed to
insufficient strength of base paper can be prevented. The ash content is
more preferably 10 mass % to 20 mass %, both inclusive.

[0042] In the present invention, the ash content is a ratio (mass %) of
the mass of incombustibles remaining after the paper substrate undergoes
a combustion treatment at 500° C. for 1 hour to the absolute dry
mass of the paper substrate before the combustion treatment. The ash
content may be controlled by controlling the content of components such
as the filler in the paper substrate.

[0043] In the present invention, the thickness of the paper substrate is
not particularly limited. The thickness of the paper substrate is
preferably 50 μm to 300 μm, both inclusive, and more preferably 60
μm to 250 μm, both inclusive.

[0044] In the printing paper of the present invention, an optional
cationic resin, and a multivalent cation salt are attached onto the paper
substrate. The total amount of the cationic resin and the multivalent
cation salt attached on both surfaces of the paper substrate is 1.0
g/m2 to 5.0 g/m2, both inclusive. The mass ratio of the
cationic resin to the multivalent cation salt is 0:100 to 90:10, both
inclusive.

[0045] The printing paper of the invention optionally includes a cationic
resin as required. The cationic resin reacts with an anionic moiety of a
dye ink to fix the dye ink and to provide water resistance of images
created with the aqueous dye ink. As a result, it is possible to improve
the water resistance of images that are created with aqueous dye inks
used in ink jet printing which contain direct dyes or acid dyes.

[0046] The cationic resin which may be used in the invention is any of
general cationic polymers or cationic oligomers without limitation.
Preferred cationic resins are polymers or oligomers that contain a
primary to tertiary amine or a quaternary ammonium salt which allows a
proton to be easily coordinated thereto and which is ionized in water to
provide the cationic property. Specific examples of the cationic resin
include, although not limited to, compounds such as polyethyleneimine,
polyvinylpyridine, polyaminesulfone, polydialkylaminoethyl methacrylate,
polydialkylaminoethyl acrylate, polydialkylaminoethyl methacrylamide,
polydialkylaminoethyl acrylamide, polyepoxyamine, polyamidoamine,
dicyandiamide-formalin condensate, polyvinylamine and polyallylamine as
well as hydrochlorides of these compounds, polydiallyldimethylammonium
chloride, copolymers of diallyldimethylammonium chloride and a monomer
such as acrylamide, polydiallylmethylamine hydrochloride, and
dimethylamine-epichlorohydrin polycondensate. A more preferred cationic
resin is dimethylamine-epichlorohydrin polycondensate. In the present
invention, the average molecular weight of the cationic resin is not
particularly limited, but is preferably 500 to 20,000, both inclusive,
more preferably 1,000 to 10,000, both inclusive. In a preferred
embodiment of the present invention, the cationic resin is
dimethylamine-epichlorohydrin polycondensate. According to such a
preferred embodiment, in particular, the printing paper achieves
well-balanced ink jet printability.

[0047] The printing paper of the invention includes a multivalent cation
salt. The multivalent cation salt fixes an ink by its multivalent cation.
Thus, similarly to the cationic resin, this component is effective for
fixing aqueous dye inks and for providing water resistance of images
created with the aqueous dye inks. Further, this component exhibits a
high effect also in the fixation of aqueous pigment inks.

[0048] The multivalent cation salt used in the present invention is a
water-soluble salt containing a multivalent cation, and is preferably a
salt of a multivalent cation which can be dissolved in 20° C.
water at 1 mass % or more. Examples of the multivalent cations include
divalent cations such as magnesium, calcium, strontium, barium, nickel,
zinc, copper, iron, cobalt, tin and manganese, trivalent cations such as
aluminum ion, iron and chromium, tetravalent cations such as titanium and
zirconium, and complex ions of these ions. The anion forming the salt
with the multivalent cation may be any of inorganic acids and organic
acids without limitation. Examples of the inorganic acids include,
although not limited to, hydrochloric acid, nitric acid, phosphoric acid,
sulfuric acid, boric acid and hydrofluoric acid. Examples of the organic
acids include, although not limited to, formic acid, acetic acid, lactic
acid, citric acid, oxalic acid, succinic acid and organosulfonic acid.
Preferred examples of the multivalent cation salts include calcium salts
such as calcium chloride, calcium formate, calcium nitrate and calcium
acetate. Calcium chloride is more preferable.

[0049] In a preferred embodiment of the present invention, the multivalent
cation salt is a calcium salt. The reason why a calcium salt is
preferable is probably as follows. In an aqueous solution, a calcium salt
gives calcium ions, which easily form poorly water-soluble calcium salts
such as calcium hydroxide and calcium carbonate. It may be said that
uneven printing is ascribed to nonuniform ink fixation and nonuniform
speeds of ink absorption. In addition to the fact that this multivalent
cation salt, namely, a calcium salt, provides ink fixation as described
above, the calcium salt microscopically forms a poorly water-soluble
calcium salt on the surface of the calcium carbonate in an area of the
paper substrate in which the area exhibits low ink absorption properties,
and such a poorly water-soluble calcium salt probably allows a capillary
phenomenon to occur. Thus, it is necessary that the paper substrate
contain calcium carbonate. Such effects produced by a calcium salt are
larger than by any of other multivalent cation salts.

[0050] In a preferred embodiment of the invention, the calcium salt is
calcium chloride. Calcium chloride is highly effective for the
suppression of the occurrence of uneven printing during ink jet printing
probably because of its high moisture absorptivity.

[0051] In the present invention, the total amount of the optional cationic
resin, and the multivalent cation salt attached on both surfaces of the
paper substrate is in the range of 1.0 g/m2 to 5.0 g/m2, both
inclusive, in terms of the amount of attached solids. Any smaller amount
than the above range may lead to a failure to obtain sufficient water
resistance or abrasion resistance of images. The effects in the
improvements of ink absorption properties, water resistance of images,
abrasion resistance of images and the suppression of uneven printing are
saturated even if the amount is larger than the above range, thus causing
cost disadvantages.

[0052] In the present invention, the mass ratio of the cationic resin to
the multivalent cation salt is in the range of 0:100 to 90:10, both
inclusive. In ink jet printing with an ink jet printing machine, the
cationic resin tends to provide excellent water resistance of images
created with aqueous dye inks. The multivalent cation salt tends to
provide excellent abrasion resistance of images created with aqueous
pigment inks and to suppress the occurrence of uneven printing when
images are printed with aqueous pigment inks, and also tends to allow
images formed with aqueous dye inks to exhibit high water resistance.
Accordingly, the printing paper containing the cationic resin and the
multivalent cation salt with the above mass ratio can achieve
well-balanced suitability for both aqueous dye inks and aqueous pigment
inks. In a preferred embodiment of the present invention, the mass ratio
of the cationic resin to the multivalent cation salt is 10:90 to 80:20,
both inclusive.

[0053] The printing paper of the invention may be produced by attaching
the optional cationic resin, and the multivalent cation salt onto the
paper substrate. The cationic resin and the multivalent cation salt may
be attached onto the paper substrate by, for example, applying the
cationic resin and the multivalent cation salt to the paper substrate or
impregnating the paper substrate with the cationic resin and the
multivalent cation salt. The application may be performed with any of
various coaters such as size presses, film presses, gate roll coaters and
film transfer coaters, as well as blade coaters, rod coaters, air knife
coaters and curtain coaters. From the viewpoint of production costs, it
is preferable that the components be applied on-machine with a coater
such as a size press, a gate roll coater or a film transfer coater
installed on the papermaking machine.

[0054] The printing paper in which the cationic resin and the multivalent
cation salt are attached onto the paper substrate may be used as such.
Alternatively, the surface of the printing paper may be smoothened as
required using a device such as a on-line machine calender, a soft nip
calender or a super calender.

[0055] However, excessive calendering for smoothing results in a decreased
number of voids in the printing paper, thereby deteriorating ink
absorption properties exhibited during ink jet printing. Thus, slight
calendering is preferable. In detail, it is preferable that calendering
be performed such that the density of the calendered paper becomes not
more than 1.0 g/cm3.

[0056] The inventive printing paper may be used not only for offset
printing but also for other types of printing such as gravure printing
and others. Further, the printing paper may be used for rotary or
sheetfed industrial ink jet printing machines as well as for printers
such as commercially available ink jet printers.

[0057] Another aspect of the invention is directed to a method for forming
printed images which includes ink jet printing using a pigment ink on the
above-described printing paper at a printing speed of 60 m/min or more.
According to this method, the image quality of images printed with an ink
jet printing machine can be improved. A further aspect of the invention
is directed to a method for forming printed images on the above-described
printing paper using an offset printing machine and/or an ink jet
printing machine. According to this method, excellent printed images can
be formed using an offset printing machine and/or an ink jet printing
machine.

[0058] In all the aspects and embodiments described in the present
invention, configurations, effects and contents which are similar to
those described with respect to the first aspect and embodiment are not
described anew each time where appropriate.

EXAMPLES

[0059] Hereinbelow, the present invention will be described by presenting
Examples without limiting the scope of the invention to such Examples. In
Examples, "part(s)" and "%" refer to part(s) by mass and mass %,
respectively, unless otherwise mentioned.

(Production of Paper Substrate)

[0060] To a pulp slurry which contained 100 parts of LBKP having a
freeness of 400 mlcsf were added 15 parts of precipitated calcium
carbonate (product name: TP-121, manufactured by OKUTAMA KOGYO CO., LTD.)
as a filler, 0.8 parts of amphoteric starch (product name: Cato 3210,
manufactured by Nippon NSC Co., Ltd.), 0.8 parts of aluminum sulfate and
0.05 parts of an alkyl ketene dimer sizing agent (product name: Sizepine
K903, manufactured by Arakawa Chemical Industries, Ltd.). The resultant
paper stock was made into paper with a Fourdrinier machine, thereby
producing a paper substrate having a basis weight of 80 g/m2. The
ash content in the paper substrate was 13.0%.

Example 1

[0061] With an on-machine film transfer coater, oxidized starch (product
name: MS #3800, manufactured by NIHON SHOKUHIN KAKO CO., LTD.) and
calcium chloride as a multivalent cation salt were attached onto the
above-produced paper substrate in amounts of 2.5 g/m2 and 2.0
g/m2, respectively, in terms of the amounts of solids attached onto
both surfaces of the paper substrate. The resultant paper was on-line
machine calendered, thereby producing printing paper of Example 1.

Example 2

[0062] Printing paper of Example 2 was produced in the same manner as in
Example 1, except that calcium chloride used in Example 1 and
dimethylamine-epichlorohydrin polycondensate (product name: JET FIX 5052,
manufactured by Satoda Chemical Industrial Co., Ltd.) as a cationic resin
were attached in amounts of 1.8 g/m2 and 0.2 g/m2,
respectively, in terms of the amounts of solids attached onto both
surfaces of the paper substrate.

Example 3

[0063] Printing paper of Example 3 was produced in the same manner as in
Example 1, except that calcium chloride used in Example 1 and
dimethylamine-epichlorohydrin polycondensate (product name: JET FIX 5052,
manufactured by Satoda Chemical Industrial Co., Ltd.) as a cationic resin
were attached in amounts of 1.5 g/m2 and 0.5 g/m2,
respectively, in terms of the amounts of solids attached onto both
surfaces of the paper substrate.

Example 4

[0064] Printing paper of Example 4 was produced in the same manner as in
Example 1, except that calcium chloride used in Example 1 and
dimethylamine-epichlorohydrin polycondensate (product name: JET FIX 5052,
manufactured by Satoda Chemical Industrial Co., Ltd.) as a cationic resin
were attached in amounts of 1.0 g/m2 and 1.0 g/m2,
respectively, in terms of the amounts of solids attached onto both
surfaces of the paper substrate.

Example 5

[0065] Printing paper of Example 5 was produced in the same manner as in
Example 1, except that calcium chloride used in Example 1 and
dimethylamine-epichlorohydrin polycondensate (product name: JET FIX 5052,
manufactured by Satoda Chemical Industrial Co., Ltd.) as a cationic resin
were attached in amounts of 0.5 g/m2 and 1.5 g/m2,
respectively, in terms of the amounts of solids attached onto both
surfaces of the paper substrate.

Example 6

[0066] Printing paper of Example 6 was produced in the same manner as in
Example 1, except that calcium chloride used in Example 1 and
dimethylamine-epichlorohydrin polycondensate (product name: JET FIX 5052,
manufactured by Satoda Chemical Industrial Co., Ltd.) as a cationic resin
were attached in amounts of 0.2 g/m2 and 1.8 g/m2,
respectively, in terms of the amounts of solids attached onto both
surfaces of the paper substrate.

Example 7

[0067] Printing paper of Example 7 was produced in the same manner as in
Example 1, except that calcium chloride used in Example 1 was attached in
an amount of 4.0 g/m2 in terms of the amount of solids attached onto
both surfaces of the paper substrate.

Example 8

[0068] Printing paper of Example 8 was produced in the same manner as in
Example 1, except that calcium chloride used in Example 1 and
dimethylamine-epichlorohydrin polycondensate (product name: JET FIX 5052,
manufactured by Satoda Chemical Industrial Co., Ltd.) as a cationic resin
were attached in amounts of 3.6 g/m2 and 0.4 g/m2,
respectively, in terms of the amounts of solids attached onto both
surfaces of the paper substrate.

Example 9

[0069] Printing paper of Example 9 was produced in the same manner as in
Example 1, except that calcium chloride used in Example 1 and
dimethylamine-epichlorohydrin polycondensate (product name: JET FIX 5052,
manufactured by Satoda Chemical Industrial Co., Ltd.) as a cationic resin
were attached in amounts of 3.0 g/m2 and 1.0 g/m2,
respectively, in terms of the amounts of solids attached onto both
surfaces of the paper substrate.

Example 10

[0070] Printing paper of Example 10 was produced in the same manner as in
Example 1, except that calcium chloride used in Example 1 and
dimethylamine-epichlorohydrin polycondensate (product name: JET FIX 5052,
manufactured by Satoda Chemical Industrial Co., Ltd.) as a cationic resin
were attached in amounts of 2.0 g/m2 and 2.0 g/m2,
respectively, in terms of the amounts of solids attached onto both
surfaces of the paper substrate.

Example 11

[0071] Printing paper of Example 11 was produced in the same manner as in
Example 1, except that calcium chloride used in Example 1 and
dimethylamine-epichlorohydrin polycondensate (product name: JET FIX 5052,
manufactured by Satoda Chemical Industrial Co., Ltd.) as a cationic resin
were attached in amounts of 1.0 g/m2 and 3.0 g/m2,
respectively, in terms of the amounts of solids attached onto both
surfaces of the paper substrate.

Example 12

[0072] Printing paper of Example 12 was produced in the same manner as in
Example 1, except that calcium chloride used in Example 1 and
dimethylamine-epichlorohydrin polycondensate (product name: JET FIX 5052,
manufactured by Satoda Chemical Industrial Co., Ltd.) as a cationic resin
were attached in amounts of 0.4 g/m2 and 3.6 g/m2,
respectively, in terms of the amounts of solids attached onto both
surfaces of the paper substrate.

Example 13

[0073] Printing paper of Example 13 was produced in the same manner as in
Example 1, except that calcium chloride used in Example 1 and
dimethylamine-epichlorohydrin polycondensate (product name: JET FIX 5052,
manufactured by Satoda Chemical Industrial Co., Ltd.) as a cationic resin
were attached in amounts of 0.5 g/m2 and 0.5 g/m2,
respectively, in terms of the amounts of solids attached onto both
surfaces of the paper substrate.

Example 14

[0074] Printing paper of Example 14 was produced in the same manner as in
Example 1, except that calcium chloride used in Example 1 and
dimethylamine-epichlorohydrin polycondensate (product name: JET FIX 5052,
manufactured by Satoda Chemical Industrial Co., Ltd.) as a cationic resin
were attached in amounts of 1.5 g/m2 and 1.5 g/m2,
respectively, in terms of the amounts of solids attached onto both
surfaces of the paper substrate.

Example 15

[0075] Printing paper of Example 15 was produced in the same manner as in
Example 1, except that calcium chloride used in Example 1 and
dimethylamine-epichlorohydrin polycondensate (product name: JET FIX 5052,
manufactured by Satoda Chemical Industrial Co., Ltd.) as a cationic resin
were attached in amounts of 2.5 g/m2 and 2.5 g/m2,
respectively, in terms of the amounts of solids attached onto both
surfaces of the paper substrate.

Example 16

[0076] Printing paper of Example 16 was produced in the same manner as in
Example 4, except that calcium chloride used in Example 4 was replaced by
calcium formate.

Example 17

[0077] Printing paper of Example 17 was produced in the same manner as in
Example 10, except that calcium chloride used in Example 10 was replaced
by calcium formate.

Example 18

[0078] Printing paper of Example 18 was produced in the same manner as in
Example 4, except that calcium chloride used in Example 4 was replaced by
calcium nitrate.

Example 19

[0079] Printing paper of Example 19 was produced in the same manner as in
Example 10, except that calcium chloride used in Example 10 was replaced
by calcium nitrate.

Example 20

[0080] Printing paper of Example 20 was produced in the same manner as in
Example 4, except that calcium chloride used in Example 4 was replaced by
magnesium sulfate.

Example 21

[0081] Printing paper of Example 21 was produced in the same manner as in
Example 10, except that calcium chloride used in Example 10 was replaced
by magnesium sulfate.

Example 22

[0082] Printing paper of Example 22 was produced in the same manner as in
Example 4, except that the dimethylamine-epichlorohydrin polycondensate
(product name: JET FIX 5052, manufactured by Satoda Chemical Industrial
Co., Ltd.) used in Example 4 was replaced by an acrylamide-diallylamine
copolymer (product name: SUMIREZ resin 1001, manufactured by Sumitomo
Chemical Co., Ltd.).

Example 23

[0083] Printing paper of Example 23 was produced in the same manner as in
Example 10, except that the dimethylamine-epichlorohydrin polycondensate
(product name: JET FIX 5052, manufactured by Satoda Chemical Industrial
Co., Ltd.) used in Example 10 was replaced by an acrylamide-diallylamine
copolymer (product name: SUMIREZ resin 1001, manufactured by Sumitomo
Chemical Co., Ltd.).

Comparative Example 1

[0084] With an on-machine film transfer coater, oxidized starch (product
name: MS #3800, manufactured by NIHON SHOKUHIN KAKO CO., LTD.) alone was
attached onto the paper substrate in an amount of 2.5 g/m2 in terms
of the amount of solids attached onto both surfaces of the paper
substrate. The resultant paper was on-line machine calendered, thereby
producing printing paper of Comparative Example 1.

[0086] Printing paper of Comparative Example 3 was produced in the same
manner as in Comparative Example 2, except that the
dimethylamine-epichlorohydrin polycondensate (product name: JET FIX 5052,
manufactured by Satoda Chemical Industrial Co., Ltd.) used in Comparative
Example 2 was attached in an amount of 4.0 g/m2 in terms of the
amount of solids attached onto both surfaces of the paper substrate.

Comparative Example 4

[0087] Printing paper of Comparative Example 4 was produced in the same
manner as in Example 1, except that calcium chloride used in Example 1
was attached in an amount of 0.5 g/m2 in terms of the amount of
solids attached onto both surfaces of the paper substrate.

Comparative Example 5

[0088] Printing paper of Comparative Example 5 was produced in the same
manner as in Example 1, except that calcium chloride used in Example 1
and dimethylamine-epichlorohydrin polycondensate (product name: JET FIX
5052, manufactured by Satoda Chemical Industrial Co., Ltd.) as a cationic
resin were attached in amounts of 0.25 g/m2 and 0.25 g/m2,
respectively, in terms of the amounts of solids attached onto both
surfaces of the paper substrate.

[0089] The printing papers of Examples 1 to 23 and Comparative Examples 1
to 5 were tested by the following methods to evaluate properties. The
results are shown in Table 1.

<Offset Printability>

[0090] Images were printed over a length of 6000 m with an offset form
rotary press manufactured by Miyakoshi Printing Machinery Co., Ltd. under
conditions where the printing speed was 150 m/min, the inks used were T&K
TOKA UV BEST CURE black and bronze red, and UV radiation value: 8
kW×2 irradiators. After printing, the occurrence of blanket piling
and the quality of the print sample were visually inspected and
evaluated. Practical use is possible without any problems when the print
is graded 3 to 5.

[0091] 5: Very good

[0092] 4: Good

[0093] 3: Practically usable

[0094] 2: Bad

[0095] 1: Very bad

<Ink Absorption Property (Dye Inks)>

[0096] Evaluation images were printed with dye inks at 150 m/min using ink
jet printing machine New MJP-600 (model: MJP-20C) manufactured by
Miyakoshi Printing Machinery Co., Ltd. Printing was performed in such a
manner that 2 cm×2 cm square solid patterns were recorded in a
single continuous row with seven colors, namely, black, cyan, magenta,
yellow, and superimposed colors (red, green, blue) created by a
combination of two colors out of the above three color inks except black.
The printed section was visually inspected to evaluate the solid color
portions and the boundaries. Practical use is possible without any
problems when the print is graded 3 to 5.

[0097] 5: The boundaries between colors were free from bleeding.

[0098] 4: The boundaries between colors were substantially free from
bleeding.

[0099] 3: A boundary between colors had become blurred but was still
clearly recognizable.

[0100] 2: A boundary between colors was unclear, and adjacent colors had
bled slightly across the boundary.

[0101] 1: Each of the boundaries between colors was indistinct, and colors
had bled to adjacent colors markedly.

<Water Resistance of Images (Dye Inks)>

[0102] Evaluation images were printed with dye inks at 150 m/min using ink
jet printing machine New MJP-600 (model: MJP-20C) manufactured by
Miyakoshi Printing Machinery Co., Ltd. 50% Halftone dot patterns and
characters were printed with each of black, cyan, magenta and yellow. The
printed section was allowed to stand for 24 hours and thereafter soaked
in water for 30 seconds. After excess water was removed with filter
paper, the printed paper was allowed to dry naturally. The print was
inspected for bleeding by visual evaluation. Practical use is possible
without any problems when the print is graded 3 to 5.

[0103] 5: There was no bleeding.

[0104] 4: Slight bleeding had been caused, but was ignorable.

[0105] 3: Although there was bleeding, the halftone dots and the
characters were clearly recognizable.

[0106] 2: Bleeding had occurred. The halftone dots and the characters were
unclear and appeared blurred.

[0107] 1: Severe bleeding had occurred. The halftone dots and the
characters were very unclear.

<Ink Absorption Property (Pigment Inks)>

[0108] Evaluation images were printed with pigment inks at 75 m/min using
ink jet printing machine Versamark VL2000 manufactured by Eastmen Kodak
Company. Printing was performed in such a manner that 2 cm×2 cm
square solid patterns were recorded in a single continuous row with seven
colors, namely, black, cyan, magenta, yellow, and superimposed colors
(red, green, blue) created by a combination of two colors out of the
above three color inks except black. The printed section was visually
inspected to evaluate the solid color portions and the boundaries.
Practical use is possible without any problems when the print is graded 3
to 5.

[0109] 5: The boundaries between colors were free from bleeding.

[0110] 4: The boundaries between colors were substantially free from
bleeding.

[0111] 3: A boundary between colors had become blurred but was still
clearly recognizable.

[0112] 2: A boundary between colors was unclear, and adjacent colors had
bled slightly across the boundary.

[0113] 1: Each of the boundaries between colors was indistinct, and colors
had bled to adjacent colors markedly.

<Abrasion Resistance of Images (Pigment Inks)>

[0114] Evaluation images were printed with a pigment ink at 75 m/min using
ink jet printing machine Versamark VL2000 manufactured by Eastman Kodak
Company. An 18 cm×18 cm solid pattern of black ink was tested by
being rubbed one time with a cotton gauze under a load of 500 g or 300 g
after 24 hours after the pattern was printed. Practical use is possible
without any problems when the print is graded 3 to 5.

[0115] 5: Substantially no flaws were caused under a load of 500 g.

[0116] 4: Slight flaws were caused under a load of 500 g, but the level of
the flaws was acceptable.

[0117] 3: Slight flaws were caused under a load of 300 g, but the level of
the flaws was acceptable.

[0118] 2: Some flaws were caused under a load of 300 g.

[0119] 1: Severe flaws were caused under a load of 300 g.

<Uneven Printing (Pigment Inks)>

[0120] Evaluation images were printed with pigment inks at 75 m/min using
ink jet printing machine Versamark VL2000 manufactured by Eastman Kodak
Company. Printing was performed in such a manner that 3 cm×3 cm
square solid patterns were recorded in a single continuous row with seven
colors, namely, black, cyan, magenta, yellow, and superimposed colors
(red, green, blue) created by a combination of two colors out of the
above three color inks except black. The printed section was visually
inspected to evaluate the unevenness in print density of each of the
solid color portions. Practical use is possible without any problems when
the print is graded 3 to 5.

[0121] 5: Any unevenness in print density was not found.

[0122] 4: Very slight unevenness in print density was found for one or
more colors.

[0123] 3: Slight unevenness in print density was found.

[0124] 2: Unevenness in print density was found locally.

[0125] 1: Unevenness in print density was found in the entirety of the
printed section.

[0126] From Table 1, it has been illustrated that the printing paper
exhibits an excellent balance between offset printability and the
evaluation items of ink jet printability when the printing paper
includes, as main components, a paper substrate containing cellulose pulp
and calcium carbonate as a filler, and an optional cationic resin, and a
multivalent cation salt attached onto the paper substrate, wherein the
total amount of the cationic resin and the multivalent cation salt
attached on both surfaces is 1.0 g/m2 to 5.0 g/m2, both
inclusive, and the mass ratio of the cationic resin to the multivalent
cation salt is 0:100 to 90:10 both inclusive. Further, it has been shown
that the printing paper exhibits a further improved balance between
offset printability and the evaluation items of ink jet printability when
the ratio of the cationic resin to the multivalent cation salt is 10:90
to 80:20, both inclusive.

[0127] From the comparison of Examples 4 and 10 with Examples 22 and 23,
it has been shown that a particularly excellent balance in the evaluation
items of ink jet printability is obtained when the printing paper
contains dimethylamine-epichlorohydrin polycondensate as the cationic
resin. Further, the comparison of Examples 4, 10, 16, 17, 18 and 19 with
Examples 20 and 21 illustrates that the printing paper achieves a
particularly excellent balance in the evaluation items of ink jet
printability when a calcium salt is used as the multivalent cation salt.
It has been further shown from Examples 4 and 10 compared to Examples 16
to 19 that the ink jet printability is best balanced when calcium
chloride is used as the calcium salt.

[0128] On the other hand, Comparative Examples 1 to 5 which did not
satisfy the conditions according to the invention failed to achieve the
advantageous effects of the invention.